Stress Spikes in Pin and Hanger System of Truss Bridge

Several functional problems have been reported on pin and hanger system truss bridges, such as frozen pins, stress spikes in hangers, lack of expansion joint movements, etc. It has been difficult to develop a pin and hanger retrofit strategy because the cause for the observed problems is usually unknown. This paper presents a study performed on the pin and hanger system of one such bridge—the Newburgh Beacon bridge. Extensive field testing performed so far has failed to identify the cause for the observed stress spikes. The concept of misalignment loading is developed in this article to explain the observed behavior. Stress spikes predicted using this concept matched very well with the observed stress spikes. Finally, the use of misalignment loading to evaluate other truss members is also discussed.